Ionization differences between weak and strong electrolytes: the role of protonic quantum effects as perturbed by dielectric relaxation spectroscopy

Revealing the microscopic dynamics, including protonic quantum effects, in aqueous electrolyte solutions has been a challenge for modern experimental methods and molecular dynamics simulations of the past decade. These properties are out of the scope of the standard electrolytic dissociation model and leave a gap between theory and experiment due to the lack of details of the fast molecular dynamics during solvation. We report a dielectric-spectroscopy study (1Hz to 20 GHz), which unambiguously demonstrates a net difference in the dynamic structures of weak and strong electrolytes, shedding new light on the mechanism of solvation via proton exchange reactions. Based on these data, we suggest an extension of Arrhenius’ seminal model, providing a more accurate description of the electrical properties of electrolytes over a wide range of concentrations (10$^{-7}$ to 10 M). We show that dissolved species of weak electrolytes more likely interact with each other than with the solvent, preventing dissociation and explaining a sharp difference between weak and strong electrolytes. These results extend our understanding of the molecular dynamics of aqueous electrolyte solutions in biology, electrochemical systems, and nanofluidics.